Sedimentation and composition of wall communities in Alaskan fjords

Abstract

The effects of suspended sediments on the composition of wall communities in Alaskan fjords were investigated by quantitative assessment of underwater photo-quadrats. In fjords with actively retreating tidewater glaciers, suspended sediment levels were extremely high at the heads and were exponentially lower at the mouths. Fjords without glaciers had low suspended sediment levels throughout. The per cent cover and number of species were lowest where sedimentation was highest, at the heads of glacial fjords. Here the wall communities were dominated by a sparse cover of small serpulid worms. Richer communities comprising mostly algae, sponges, hydroids, bryozoans, tunicates and brachiopods were found in fjords without glaciers, and at the mouths of glacial fjords. There was a positive correlation between water clarity and community composition along a gradient from heads to the mouths of fjords with high suspended sediment levels.